Diffusion barrier layer with a high barrier effect

ABSTRACT

The invention relates to an organic diffusion barrier layer ( 58 ) applied to a substrate ( 44 ). Said barrier layer has an apolar skeletal structure and a high barrier effect with respect to volatile gases, vapors and liquids. The diffusion barrier layer ( 58 ) consists of a hydrocarbon polymer that is produced by means of plasma polymerization. It respectively contains 0.01-6 at % of at least one element from the group consisting of oxygen, nitrogen, fluorine, bromine, boron and silicon, whereby the total amount of said elements does not exceed 12 at %. The barrier effect of the diffusion barrier layer ( 58 ) is produced by means of at least one pulsed or continuous DC magnetron sputtering source plasma ( 26 ) or by means of inductively excited, pulsed or continuous microwave discharge ( 20 ).

The present invention concerns a substrate with a deposited organicdiffusion barrier layer. The invention also concerns a process forproduction of a substrate with a diffusion barrier layer and usesthereof.

The storage of foodstuffs, drugs, delicate materials andmicro-electronic components for a lengthy period taking into accountambient influences is a vital problem of our time. New materials andprocesses to protect the stored materials against permeation of damaginggases and vapours, e.g. oxygen and water vapour, must be used in orderto protect the stored materials. Plastic films as a highly functionalpackaging medium are already used in many places as a substitute formetal and glass elements. Taking into account environmental protectionaspects, chemically inert and transparent films of polyethyleneterephthalate (PET), polypropylene (PP) or polyethylene (PE) and plasticfilms with similar action are used to a great extent. If these films aredamaged for example by heat, no toxic vapours occur. The properties ofconventional PET, PP or PE films are not, however, such that they canadequately protect delicate materials as described above. For thisreason in the known manner laminate structures of several layers ofpolymers, for example ethyl vinyl alcohol (EVOH), are used in order tocompensate for the relatively low barrier properties of the individualcoatings against gases.

Also, according to known processes plastic films are coated with thindiffusion blocking or barrier layers which consist of metal or metaloxides. These coatings must be thin, elastic and free from pores(pinholes) or hairline cracks (microcracks) and must not lose theirpermeation properties even over a long storage period.

Metal oxide barrier layers are optically transparent,microwave-compatible, and fulfil the ecological requirements, butbecause of their rigidity their area of application is rather limited.Plasma-polymerised coatings with compounds containing fluorine orsulphur allow the reduction of solvent permeation in plastic containers.Also, multilayer systems have been developed consisting of oxide-likebarrier layers embedded in polymer-like materials.

Thin hydrocarbon barrier coatings have proved good alternatives tostiff, brittle metal oxide barrier layers, as described for example inWO,A1 96/28587 and EP,A1 0739655. These thin hydrocarbon coatings arepreferably produced by means of DC magnetron discharge processes, highfrequency or microwave discharge.

DE,A1 4316349 also describes the production of diffusion barrier layersin hollow bodies, where this is achieved by means of a microwaveprocess.

The two European patent specifications EP,B1 0381110 and 0381111 proposethe production of a protective coating for electroactive passivatecoating of semi-conductor elements generated by means of a highfrequency low pressure plasma deposition of gaseous hydrocarbons.

U.S. Pat. No. 5,041,303 describes the production of inorganic anddiamond-like diffusion barrier layers which are produced by means ofelectromagnetic energy in the microwave frequency range. Finally EP,B10575299 describes the production of a barrier film by means of highfrequency plasma process, where the barrier layer is deposited in avacuum chamber from a plasma generated from non-saturated hydrocarbons,amongst others.

EP-A1 0176636 discloses a thin polymerised film of high density, highhardness and high strength. This layer is deposited on the surface of asubstrate by plasma polymerisation. The gas used to generate the plasmacontains a halogenated alkane and/or an alkane with either hydrogenand/or a halogen. The atomic ratio halogen/hydrogen in the gas lies inthe range of 0.1:1 to 5:1. The plasma temperature lies in the reactionzone range at 6000° K. or higher but below 30,000° K. The pressureduring polymerisation is 0.001 to 1 Torr. The thin polymer layer is usedas a protective coating for numerous objects, also as a harder surface,rust protection coating, scratch protection, gas barrier etc. Theprotective coating is particularly suitable as a protective film formagnetic data carriers.

In particular, in the area of application described above, storage ofcommodities, for example delicate drugs or similar, it is important thatthe permeation of oxygen and other gases is low or almost zero and thisimpermeability remains guaranteed even at high ambient humidity. It isquite possible, using the metal oxide coatings described in the state ofthe art, to generate a high oxygen barrier effect but usually thisdiminishes greatly, i.e. the oxygen permeation increases, as the ambientor relative humidity rises. In particular, in tropical zones this trendconstitutes a major problem which can lead to premature degradation offoodstuffs and drugs.

The task of the present invention is to create a substrate with animproved diffusion barrier layer which has better barrier propertiesagainst oxygen and other gases, in particular at high ambient humidity.

According to the invention the task is solved with regard to a substratewith a diffusion barrier based on carbon and hydrogen at a content of20-80 at % of both elements, whereby the barrier effect of the diffusionbarrier layer is sustained even in damp air.

Preferably, in the diffusion barrier layer at least one element of thegroup according to the paragraph above has a content of 0.1-3 at %.

The diffusion barrier layer is constructed on the basis of carbon andhydrogen, preferably with a content of 20-80 at % but in particular30-70 at %.

The diffusion barrier layer as stated is preferably largely ahydrocarbon plasma polymer with non-polar basic structure, i.e. thediffusion barrier layer is produced by plasma polymerisation of at leastone hydrocarbon monomer, preferably with maximum 8 C-atoms, with inertgases mixed in. The diffusion barrier layer can be produced by means ofthe plasma of a magnetron sputtering source or by combination of thesputtering source with the plasma-induced gas phase polymerisation.Alternatively, the barrier layer can be produced by means of inductivelycoupled microwave discharge.

When DC magnetron sputtering plasma is used, it has proved advantageousto overlay this with a plasma-induced gas phase polymerisation and applyan LF/HF (10 kHz-100 MHz) induced negative bias potential to thesubstrate.

In the case of a microwave discharge, it has proved advantageous for thehydrocarbon gas-inert gas mixture to be processed with a surplus ofhydrocarbon gas. The inert gas can be helium, neon, argon or other inertgases as pure gases, but according to a preferred embodimentadvantageously a mixture of argon and helium is used.

When a magnetron sputtering source is used, preferably ahydrocarbon-inert gas mixture is used, the latter in particular in theform of helium, neon and/or argon.

With reference to the plasma polymerisation for production of asubstrate with diffusion barrier layer, the task is solved according tothe invention in that the barrier layer is produced by means of at leastone pulsed or continuous DC magnetron sputtering source plasma or bymeans of inductively coupled pulsed or continuous microwave discharge.

Preferably, the reactor is first evacuated to a pressure below 5.10⁻³mbar, preferably below 1.10⁻⁴ mbar, then the reaction gases added untila value not above 1 bar, preferably not above 10 mbar, is reached andmaintained. The power of the energy source with a sample diameter ofaround 12 cm is suitably 50-1000 W, in particular maximum around 500 W.

For the process according to the invention a wide range of reactive gascomponents can be used in particular an alkane, alkene or alkyne and/ormixtures thereof, also with at least one inert gas as carrier gas. Theinert gas used in plasma polymerisation is for example helium, neon,argon or mixtures thereof. In the case of a pulsed DC magnetronsputtering source preferably helium is used, in the case of aninductively coupled microwave discharge, a mixture of argon and helium.

All reactive gas components are suitably used as pure hydrocarbon gases.In particular methane, ethane, propane or unsaturated hydrocarbons ofethane, propane, butane but also alkynes, separately or mixed with othercomponents.

The use of diffusion barrier layers according to the invention is asstated extremely wide. Preferred applications concern the coating ofpolymer materials such as in particular flexible polymer films. Thesediffusion barrier layers are extraordinarily effective protectivecoatings against gases, water vapour, aromatics, organic and inorganicvolatile compounds and liquids in particular against watery liquids. Thecoated polymer films consist for example of polypropylene, polyethylene,polyamide, amended sheet polyethylene terephthalate etc. Laminate filmsof the said polymers and objects formed, blown or deep-drawn from thefilms, such as in particular containers, are covered by the term polymerfilms.

A further use of a substrate with diffusion barrier layer according tothe invention lies in packing materials, in particular for sterilisationor pasteurisation of a product arranged in the packing. Here containersin direct contact with the foodstuff are extraordinarily important forthe inner and outer coating. Naturally moist foodstuffs are particularlydelicate, the diffusion barrier layers according to the invention areparticularly suitable for use in damp environments. Packing materialsconsist of polymers, for example polypropylene PP, polyethylene PE,polyamide PA, PET, and laminate films made from various polymermaterials, e.g. PP/PE, PET/PP, PET/PE, PE/PA. Such packing materials,e.g. foils, can be fitted i.e. coated or laminated with barrier layersaccording to the invention. Because of the good flexibility ormechanical properties of the diffusion barrier layers applied, foilscoated in this way can easily be rolled and unrolled. Also, such packingmaterials are particularly suitable for foodstuffs as no organoleptic orchemical changes to the filling according to the Foodstuffs Law canoccur. The said migration protection and perm-selectivity isparticularly important for the packing of foodstuffs as foodstuffs areoften packed under inert gas (CO₂, N₂ or mixtures thereof). The higherpermeability of CO₂ in comparison with oxygen consequently givesadditional protection to the filling. Thus, the barrier layer is oftenrequired to provide a high oxygen and water vapour barrier.

Further advantageous possible applications are listed merely in brief:

UV protection

medical engineering, protective coatings for implants, in particular inmoist environments, sterilisation and as protective coatings fortreatment instruments, sterilisation

protective coatings for ceramic material and glass-like objects, carbonand glass fibres and/or composite materials thereof, against volatileand non-volatile compounds, in particular chemicals

protective coatings for polymer strips and tapes

protective coatings for recycled products.

As well as the broad application spectrum another substantial advantageof the diffusion barrier layers according to the invention lies in theirsterilisability or pasteurisability. The following known processes canbe used in order to sterilise or pasteurise products (films, containers,coated materials) equipped with diffusion barrier layers proposedaccording to the invention:

sterilisation with water vapour and water in autoclaves up to 150° C.,in particular up to 135° C.; no mechanical damage and no subsequentdiscoloration of the coating

sterilisation with gases (ethylene oxide, H₂O₂ etc), no chemisorption oradsorption of gases on the chemically inert barrier layer

high pressure sterilisation

gamma sterilisation

high pressure, gamma and plasma sterilisation

pasteurisation at 70-100° C.

The present invention is described in more detail using design examplesshown in drawing and table form.

The drawings show diagrammatically:

FIG. 1 a CVD reactor used for plasma generation for production ofdiffusion barrier layers,

FIG. 1a a part section through a coated substrate and

FIG. 2 UV-VIS transmission spectra.

FIG. 1 shows a substantially cylindrical horizontal CVD (chemical vapourdeposition) reactor 10 which is suitable for production of a plasmanecessary for performance of the process according to the invention, inparticular a universal low temperature plasma. The CVD reactor 10 has asolid corrosion-resistant steel casing 12 and is connected to earth 14.At least one quartz window 16 in the steel casing 12 allows microwavesto be coupled into the inside of the reactor.

On the right side of the front 18 is integrated a microwave head 20which is supplied electrically by a microwave generator 22.

On the opposite left side of the front 24 of the CVD reactor is fitted aDC/HF magnetron 26 with a carbon target 27 which in turn has a screeningplate 28. The carbon target 27 preferably has a purity of at least99.9%. A relay 30 can switch from a DC generator 32 with pulse unit 34to an HF generator 36 with preset bias 38.

A pump stand is connected by way of an approximately longitudinallycentrally arranged closeable flange 40. A substrate holder 42 ispositioned inside the CVD reactor 10. On this substrate holder 42 ismounted a substrate 44 to be coated. Naturally, in industrial practice awhole battery of substrates 44 is fitted in the CVD reactor 10.

The substrate holder 42 is connected to the bias 38 by way of a furtherrelay 46. When relay 46 switches, the substrate holder 42 is earthed.

A gas system 48 in the present case comprises four gas supply lines 50each with a controllable valve 52 for supplying reaction and carriergases. The gas system 48 is also structured in the known manner, beingsupplied by way of the cylindrical steel casing 12. A branch line 54leads to the quartz window 16 of the microwave head 20.

The CVD reactor 10 is evacuated by a pre-vacuum pump 60 with apreconnected turbo pump 62, by way of a butterfly control valve 64 whichis electromagnetically operated.

Finally, into the CVD reactor 10 through the cylinder casing of thesteel casing 12 is introduced a pressure measurement device 56 which ishighly sensitive and can measure pressures down to the range of 1.10⁻⁹mbar.

A CVD reactor 10 is suitable for performance of all processingprocedures according to the invention using various gases and mixturesthereof, flow rates, working pressures and other known and tested plasmaprocess parameters. Production processes are possible in the frequencyrange from 10 kHz to 100 GHz and in DC operation while a negativepotential is applied by way of the bias 38 to the substrate 44 or thisis connected to earth 14.

The reaction start pressure in the reactor is around 10⁻² mbar. Thepower for a specimen of diameter of approximately 12 cm is 50 to 1000 W,microwave or DC starting power. In the case of the DC magnetron 26sputtering process, a carbon target 27 of a purity of at least 99.9%(quality: pure) and a continuous electrical supply of energy or a pulsefrequency of approximately 25 kHz are selected, the microwave dischargesare also performed by continuous or pulsed mode.

FIG. 1a shows a part section through a substrate 44, coated in a CVDreactor 10 according to FIG. 1, in the form of a flexible polymer filmwith a diffusion barrier layer 58 of a thickness d of around 100 nm.

FIG. 2 shows the transmission spectra of an uncoated BOPP (biaxialoriented polypropylene) film around 20 μm thick and three coated BOPPfilms 44 approximately 50 nm thick. The abscissa shows the wavelength ofthe UV radiation in nm and the ordinate the transmission in percent. Theuncoated BOPP film shown with dotted lines, like the three coated BOPPfilms, shows a marked drop in transmission in the area of a UVwavelength of around 200 nm. At longer wavelengths above 200 nm all fourcurves rise relatively steeply, that of the uncoated BOPP film hasalready reached around 90% of the complete transmission at around 300 nmwavelength. After leaving this UV-B range, the curve for the uncoatedBOPP film remains largely constant, the curves of the three coated BOPPfilms continue to rise relatively steeply in this UV-A range. Above theUV-A range, in the VIS range above 400 nm wavelength with visible light,the three said curves rise less steeply. The range above 800 nmwavelength is not considered further here.

Characteristic properties of the three selected coatings A, B and C inFIG. 2 are given in Table 1, e.g. as further optical properties therefractive index and the total light permeability are given. Forlight-sensitive foodstuffs the conservability can be increased further.A corresponding increase in coating thickness would reinforce thiseffect further.

The following Tables 1 to 3 give the properties of various diffusionbarrier layers 58 (FIG. 1a) and their production conditions. Table 2lists the permeation properties of the hydrocarbon barrier layers atvarious relative humidities. Finally, table 3 shows the perm-selectivityi.e. the different permeabilities for gases, of pure hydrocarboncoatings.

TABLE 1 Selected Coatings Thickness Flexibility Spec OXTR² OXTB²WVTR^(c) [nm] [%] CO₂-TR⁸ N₂TR⁸ A <1.1 ± .2 <1.1 ± .2 <0.6 ± .2  20 ±2 >2.5 ± .2 24.0 ± .2 2.0 ± .3 B <14.2 ± .2  — <14.2 ± .2   58 ± 2 >6.1± .2 — — C <1.1 ± .2 <0.7 ± .2 <0.4 ± .2  73 ± 2 >2.8 ± .2 14.0 ± .4 2.0± .3 C¹ <2.1 ± .2 — —  93 ± 2 >3.71 ± .2 — — C² <3.1 ± .2 <2.05 ± .2 <5.6 ± .2  62 ± 2 >3.41 ± .2 15.0 ± .3 2.0 ± .3 C³ <39.3 ± .2  <18.7 ±.2  <12.6 ± .2   35 ± 2 >8.8 ± .2 — — D <1.0 ± .2 <1.1 ± .2 <0.1 ± .2114 ± 2 >1.9 ± .2 21.0 ± .3 7.0 ± .3 E  1.1 ± .2 <1.1 ± .2 <0.2 ± .2 131± 2 >2.2 ± .2 — — F <0.8 ± .2 <0.7 ± .2 <0.1 ± .2  16 ± 2 >1.8 ± .2 — —F¹ <2.5 ± .2 <2.0 ± .2 <1.9 ± .2 140 ± 2 >2.3 ± .2 — — F² <3.1 ± .2 <1.9± .2 <1.0 ± .2 130 ± 2 >2.6 ± .2 — — F³ <7.4 ± .2 <3.8 ± .2 — 105 ±2 >3.8 ± .2 — — F⁴ <2.1 ± .2 <1.7 ± .2 <1.8 ± .2 110 ± 2 >2.3 ± .2 — —F⁵ <2.1 ± .2 <2.0 ± .2 <2.8 ± .2  98 ± 2 >2.9 ± .2 — — PET^(g) 133.2 ±.2  93.0 ± .2 20.3 ± 2  12 μm — 726 ± 2 18.7 ± .2  SIO_(x) ^(h)  2.6 ±.2  2.4 ± .2  0.9 ± 2   36 ± 3  1.7 ± .2  54 ± 1 1.8 ± .1 Density nγ =Chemical Composition [at %] Spec [g/cm³] 589 nm Transm C H O N F ArDischarge A 1.58 2.26 63 70.9 25.9 <0.4 <0.1 <0.1 <3.5 DC/earth B 1.22 —86 55.0 45.0 <0.1 <0.1 <0.1 <0.1 DC/earth C 1.46 1.89 77 64.5 23.3 <0.1<0.1 <0.1 <0.1 DC/bias C¹ 1.40 — — 68.2 30.7 <0.8 <0.3 <0.1 <0.1 DC/biasC² 1.51 1.51 — 70.5 28.2 <1.0 <0.3 <0.1 <0.1 DC/bias C³ 1.03 — 77 46.746.7 <6.5 <0.1 <0.1 <0.1 DC/earth D 1.39 1.86 76 67.1 32.9 <0.1 <0.1<0.1 <0.1 MW/earth E 1.44 — 74 69.0 31.0 <0.1 <0.1 <0.1 <0.1 MW/bias F1.54 1.83 76 67.6 32.4 <0.1 <0.1 <0.1 <0.1 MW/earth F¹ 1.36 — — 71.425.7 <2.7 <0.2 <0.1 <3.5 MW/earth F² — — — 73.4 23.4 <0.1 <3.2 <0.1 <0.1MW/earth F³ 1.24 — — 69.0 24.1 <0.5 <6.4 <0.1 <0.1 MW/earth F⁴ 1.32 — —69.0 28.6 <3.5 <3.5 <0.1 <0.1 MW/earth F⁵ 1.16 — — 64.1 23.1 <3.2 <9.6<0.1 <0.1 MW/earth PET^(g) —  1.576 89 MW/earth SiO_(x) ^(h) —  1.458 84Legend: a: Oxygen, carbon dioxide and nitrogen permeability[ccm(m².d.bar)]: ASTM D 3985-95 at 0% relative humidity and 23° C. b:Oxygen permeability [ccm(m².d.bar)]: ASTM D 3985-95 at 85% relativehumidity and 23° C. ^(c)Water vapour permeability [g/m_.d]: ASTMF1249-90 Standard Test Method at 90% relative humidity and 23° C.(American Society for Testing and Materials, 1997) d: Crack elongationin %: microcrack formation on a coated 12 μm PET film e: TotaI lightpermeability [CIE: Y value, 10°, D65]: ASTM D 10003-92 f: Carbon dioxideand nitrogen permeability [ccm/(m².d.bar)]: Lyssy GPM 500 at 0% relativehumidity and 23° C. ^(g)12 μm thick PET film (polyethyleneterephthalate) ^(h)36 nm SiO_(x) coated 12 μm thick PET film. DC: DCmagnetron sputter process, MW: microwave discharge. The hardness cf thecoatings lies in the range of 1-30 Vickers hardness.

TABLE 2 Summary of Permeation Properties of Pure Hydrocarbon Barrierlayers on 12 μm Thick PET Film Reduction Permeation Coating PermeationO₂ Measurement Permeation O₂ in permea- Measurement H₂O Thickness[ccm/m_*day*bar] Flexibility Coating No. Conditions [ccm/m_*day*bar]tion at r.H Condition [g/m_*day] [nm] after sterilisation [%] Process D23° C./dry 1.3 ± .1 23° C./100% r.H 0.2 ± .2 102 ± 3  3.9 ± .1 2.1 ± .2Microwave 23° C./50% r.H 1.1 ± .1 33° C./100% r.H 0.4 ± .2 108 ± 3  4.6± .1 1.8 ± .2 23° C./70% r.H 1.0 ± .1 23° C./85% r.H 0.9 ± .1 31% F 23°C./dry 1.1 ± .1 23° C./100% r.H 0.1 ± .2 96 ± 3 3.2 ± .1 1.8 ± .2Microwave 23° C./50% r.H 0.9 ± .1 33° C./100% r.H 0.3 ± .2 106 ± 3  6.3± .1 1.5 ± 2  23° C./70% r.H 0.8 ± .1 23° C./85% r.H 0.7 ± .1 36% C² 23°C./dry 3.2 ± .1 23° C./100% r.H 0.4 ± .2 55 ± 3 9.2 ± .1 >3.0 ± .2  DC23° C./50% r.H 2.5 ± .1 33° C./100% r.H 0.5 ± .2 69 ± 3 10.9 ± .2  >2.9± .2  magnetron 23° C./70% r.H 2.4 ± .1 23° C./85% r.H 1.6 ± .1 50% Ref.23° C./dry 133.2 ± .2  23° C./100% r.H 20.3 ± .2  — — — PET 23° C./50%r.H 99.8 ± .2  33° C./100% r.H 37.3 ± .2  — — — 23° C./70% r.H 95.7 ±.2  23° C./85% r.H 93.0 ± .2  30% ref. 23° C./dry 2.6 ± .1 23° C./100%r.H 0.8 ± .2 36 ± 3 64.5 ± .2  1.7 ± .2  Evaporation SiOx 23° C./50% r.H2.4 ± .1 33° C./100% r.H 0.9 ± .2 36 ± 3 78.9 ± .2  23° C./70% r.H 2.3 ±.1 23° C./85% r.H 2.4 ± .1  8%

Table 1 shows a summary of the properties of diffusion barrier layers 58(FIG. 1a) of amorphous hydrocarbon of various thicknesses on a 12 μmthick PET film. For specimens A to F⁵, for example, the oxygen, watervapour, nitrogen, carbon dioxide gas permeability, the density, therefractive index and the chemical composition are listed. Forcomparison, the corresponding values are given for an uncoated PET filmand a film coated with organic SiO_(x).

The samples shown in Table 1 are optimised coatings deposited onto PETfilm which have excellent barrier properties against water vapour,oxygen and nitrogen and to a reduced extent also against carbon dioxide.All coatings, irrespective of whether produced by DC magnetron dischargeor microwave discharge, have excellent barrier properties with lowoxygen and nitrogen contents. Comparison tests with hydrocarbon coatingswith relatively high oxygen and nitrogen contents each of >6 at % showin comparison with the invention a great increase in gas permeability ora great decrease in barrier properties.

The fact that the low oxygen permeation of non-polar hydrophobic HCcoatings is maintained or increased even at high relative humidities isshown by the results in Table 2. The two coating specimens D and F, onan increase in humidity from dry to around 85% relative humidity, show adecrease in oxygen permeation of 31% or 36%, where the microwave coatingprocess was applied. Coating sample C2 also shown in Table 1 shows adecrease of 50% in oxygen permeation from dry to 85% relative humidity,where in this case the diffusion barrier layer was produced by pulsed DCmagnetron sputtering and overlaid plasma polymerisation. An excess ofhydrocarbon gas was used during the process and a negative biaspotential applied to the substrate.

The perm-selectivity shown in Table 3 of plasma-polymerised barrierlayers is based on isostatic permeability measurements with a dry gasmixture of CO₂, O₂ and N₂ at a slightly high room temperature.

TABLE 3 Perm-selectivity of plasma-polymerised barrier layers SpecimenCO₂ O₂ N₂ N₂/O₂ CO₂/O₂ A 24.0 5.0 2.0 0.4 4.8 C 14.0 3.0 2.0 0.7 2.4 C²15.0 4.0 2.0 0.5 3.75 D 21.0 7.0 7.0 1.0 3.0 PET film 725.5 136.9 18.70.14 5.3 SiO_(x)/PET 53.8 3.4 1.8 0.53 16.0

Legend:

a. Carbon dioxide, oxygen and nitrogen permeability [ccm/(m².d.bar)]:ASTM D 3985-95 at 0% relative humidity and 23° C.

As a reference example Table 3 shows the oxygen permeation of a pure PETfilm and a PET film coated with silicon oxide. The pure PET film in thedry state has a high oxygen permeation which, however, decreases as thehumidity increases. This behaviour is material-specific, it is knownthat other polymer films do not behave in this way. In the case ofcoating with silicon oxide, the oxygen permeation reduces by only around8% on a rise in relative humidity. Consequently the polar metal oxidecoating causes a weakening in the property of PET whereas the non-polarhydrocarbon coatings have a permeation behaviour similar to PET. Asubstantial disadvantage of silicon oxide barrier layers for packing,however, is that the oxygen permeation after sterilisation, comparedwith the hydrocarbon coatings according to the invention, issunstantially higher, which is extremely unfavourable, in particular inthe case of foodstuff packing and medical technology.

In order to achieve the low content of oxygen, nitrogen fluorine,chlorine, bromine, boron and/or silicon in the diffusion barrier layerrequired according to the invention, in performance of the coatingprocesses the following conditions are required:

CVD reactor in which reproducible coatings can be

achieved (high vacuum, no gasifying components),

use of pure monomer gases or hydrocarbon gases,

use of pure inert gases e.g. helium, neon, argon etc.

If sputtering from a carbon target, it is important that a target ofpure carbon is used with a purity of >99.9%.

The process parameters claimed according to the invention and listed inTables 1 to 3, however, not only take into account high barrier effectsbut they are also selected such that at least equally good mechanicalproperties can be achieved in the coatings. As an example, andimportantly in the case of coating plastic films, the flexibility orcrack elongation % is shown in Table 1.

The diffusion barrier layers shown in table form according to theinvention are characterised in that the elongation to microcrackformation can be tailored to the product. The range for a good diffusionbarrier layer is 1 to 10% but can sometimes be more. The crackelongation naturally depends on the coating thickness which is normally10 to 1000 nm, preferably ≦300 nm, in particular 20 to 200 nm. Theflexibility of the coatings is attributable to their polymer-like naturewhich also causes excellent adhesion of the diffusion barrier layersaccording to the invention on polymer substrates. Consequently, thecoated substrates are mechanically resistant and can for example beprocessed on all possible machines for production of laminate films(wound and moulded).

In the coating of metallic or ceramic substrates, the good adhesion ofthe diffusion barrier layer is guaranteed by way of the carbon bonding.

Further properties of the multi-functional diffusion barrier layersstudied according to Tables 1 and 3 are as follows:

they are functionally stable for a long time (tested >1 year),

transparent,

microwave-compatible,

chemically resistant and hence not solvent-sensitive,

easy to laminate, in particular with conventional adhesives,

a certain degree of peelability, in particular if welded with polymermaterials such as polymer films (e.g. PET) or other materials,

absorbent in the UV range, therefore good UV protection for contents(FIG. 2),

suitable for foodstuffs as no organoleptic and chemical changes occur inthe packed product or contents,

protection against migration from packaging materials such as forexample additives or contamination, and protection against migrationfrom the product to the packing (aromatics etc),

perm-selectivity i.e. differing permeability of gases e.g. carbondioxide, nitrogen or mixtures thereof (Table 3).

For a better understanding of the invention and in particular thedevelopment of the process parameters according to the invention, theperformance of experiments for the production of Tables 1 to 3 isexplained in more detail below. Here, it proved advantageous to comparethe properties of the hydrocarbon coatings deposited on PET films whichwere deposited firstly using DC magnetron sputtering processes (plasmapolymerisation processes) and secondly by means of microwave discharges.The process parameters can however be transferred to other known plasmaprocesses.

EXAMPLE 1

In a DC magnetron discharge (continuous or bipolar pulsed) with overlaidplasma-induced gas phase polymerisation, the plasma reactor wasevacuated to a base pressure of ≦2×10⁻⁵ mbar. Carbon was sputtered fromthe carbon target, in addition by way of the gas inlets a polymerisableC_(x)H_(y) gas mixture was continuously supplied to the plasma reactor.Also, an inert gas or inert gas mixture can be introduced into theplasma chamber. The supply of energy (DC, continuous or pulsed) ignitesthe plasma. The diffusion barrier layer consisting of pure hydrocarbonis deposited onto the substrate, where the process duration and beltspeed determine the coating thickness, gas concentration, gas.

EXAMPLE 2

In a microwave discharge (pulsed or continuous; magnetic field supportedor without magnetic field) the plasma reactor was evacuated to a basepressure of ≦2×10⁻⁵ mbar. By way of the gas inlet a polymerisableC_(x)H_(y) gas mixture, which can also contain inert gases is suppliedcontinuously into the plasma reactor. The microwave energy (2, 45 GHz)(pulsed or continuous) is coupled inductively. After ignition of theplasma the required energy is set so that the pure hydrocarbon plasmacoating is deposited.

Parameters for examples 1 and 2 related to the CVD reactor shown in FIG.1.

Power: 50-1000 Watt Negative bias potential for substrate −10 to −700 VNF/HF (10 kHz-200 MHz) or DC: Working pressure: 5.10⁻³-50 mbar Gas flowC_(x)H_(y): 10-200 sccm Gas flow He, Ar: 10-200 sccm

When the process is scaled up or transferred, the parameters listed aremodified accordingly.

Analysis of Specimens

The oxygen permeability was measured at 0% relative humidity, 23° C. inaccordance with ASTM D 3985-95 using a Mocon OX-TRAN 2/20 instrument.The water vapour permeability measurements were performed with a Lyssy L80-4000 permeation tester. The total light permeability of the coatedand untreated PET films was determined according to ASTM D 10003-92(CIE: Y value 10°, D65).

The coating thickness was determined by means of a profilometer (TencorP10) on a silicon wafer. The hydrogen content, possible contaminants andthe density of the coatings were tested on coated Si (100) substratesusing Rutherford backscattering (RBS), elastic recoil detection analysis(ERDA) and x-ray photo-electronic spectroscopy (XPS).

The elastic behaviour (elongation, flexibility) was tested using aprocess based on interferometry by stretching the coated films. Themethod of measuring the elastic behaviour was developed at EMPA. Theformation of microcracks on the stretched test films and their effect onthe diffusion barrier properties were determined by a combination ofscanning electron microscopy and permeability measurements. The AFMpictures of the substrate and the coated PET films were taken at roomtemperature conditions using a Bioscope AFM (Digital Instruments) and anExplorer AFM (TopoMetrix, Model TMX 2000) in scanning mode andnon-contact mode. A periodic test of the diffusion properties wasperformed over one year on carefully selected test specimens (23° C., 0%relative humidity) to determine the long term behaviour.

Results of Film Coatings

The first half of Table 1 shows the properties of coatings (A-C³)produced by means of bipolar pulsed DC magnetron processes, and thesecond half those of coatings D to F⁵ produced by means of microwavedischarge. A correlation with the water vapour data can be noted.Furthermore, elongation values of more than 6% were achieved forcoatings with slightly lower barrier effects (OXTR: 14 cm³/m².d.bar).

An untreated PET film has a morphology consisting of 10 to 20 nm wide“clusters” and RMS roughness of around 0.8 nm. All coatings studied showa very homogeneous morphology with an RMS roughness of 1.5 to 2.5 nm anda grain size of 20-40 nm. The structure of the coated films is verysimilar and dependent neither on the discharge method nor on thedeposition parameters.

The substrate holder with specimens was both earthed and biased in thefrequency range of 10 kHz to 200 MHz. As a result of the negativepotential at the substrate, the ions in the plasma peripheral layer wereaccelerated towards the substrate so they impacted with higher energy.It is expected that the density of the coatings is higher and thepermeability values lower. However, the flexibility of the coatingsdecreases as the density increases. In addition, the deposition rateincreases due to the application of a negative potential.

What is claimed is:
 1. Substrate (44) with a deposited organic diffusionbarrier layer (58) which has a non-polar basic structure with a highbarrier effect against highly volatile gases, vapors and fluids, wherethe diffusion barrier layer (58) consists of a hydrocarbon polymerproduced by means of plasma polymerization which contains 0.01-6 at % ofat least one element of the group consisting of oxygen, nitrogen,fluorine, chlorine, bromine, boron and silicon, in total however maximum12 at %, the improvement comprising: the diffusion barrier layer basedon carbon and hydrogen has a content of 20-80 at % of both elements,whereby the barrier effect of the diffusion barrier layer (58) issustained in air having a relative humidity of 50% and higher. 2.Substrate (44) with a diffusion barrier layer (58) according to claim 1,wherein the barrier layer contains at least one element of the group ina content of 0.1-3 at %.
 3. Substrate (44) with a diffusion barrierlayer (58) according to claim 1, wherein the diffusion barrier layer(58) has a carbon and hydrogen content of each of 30-70 at %. 4.Substrate (44) with a diffusion barrier layer (58) according to claim 1,wherein the diffusion barrier layer (58) has a coating thickness of ≦300nm.
 5. Substrate (44) with a diffusion barrier layer (58) according toclaim 1, wherein the substrate (44) is a polymer material or paper, inparticular a polycarbonate, polyethylene terephthalate, polypropylene,polyethylene, polyamide or other composites thereof, coated paper,textiles, carbon fibers or a composite thereof, a ceramic material,glass or glass fibers.
 6. Process for production of a substrate (44)with a diffusion barrier layer (58) according to claim 1, wherein thebarrier layer (58) is formed by at least one of pulsed or continuous DCmagnetron sputtering source plasma (26), or by means of inductivelycoupled pulsed or continuous microwave discharge (20).
 7. Processaccording to claim 6, wherein a reactor (10) is evacuated to a pressurebelow 5.10⁻³ mbar, then reaction gases are supplied until a value nohigher than 1 bar is reached and maintained.
 8. Process according toclaim 6, wherein the power of the energy source for flat specimens ofaround 12 cm diameter is 50-1000 W.
 9. Process according to claim 7,wherein as a reactive gas component pure hydrocarbon gases are used inparticular alkanes such as methane, ethane or propane, alkenes such asethene, propene or butene or alkynes such as polypropylene, all separateor mixed with other hydrocarbon gases.
 10. Substrate (44) with adiffusion barrier layer (58) according to claim 1, wherein the substratecomprises one of a polymer material and a flexible polymer film (44)including recycled materials.
 11. Substrate (44) with a diffusionbarrier layer (58) according to claim 1, wherein the substrate comprisesone of paper, textiles, carbon fibers, ceramic material, glass, glassfibers and composites thereof.